I use these for both work and personal life - and you can edit on multiple devices…
Now, the caveat there is, it’s not entirely realtime editing …
logseq updates the display when the underlying markdown file changes, so you can edit on multiple devices if you let them sync which takes a second or so (setup that syncthing folder to watch the filesystem, instead of periodic)
So, I edit a note on my phone, walk ovee to a laptop then see the changes come in and edit some more… pick up the phone, unlock it, probably ready to edit again…
If I leave the house, syncthing could sync over the internet, but I’ve not aet that up… so in the unlikely chance that someone edits the file(s) on my laptop AND I edit on my phone, then syncthing would give me 2 files which others have explained well.
BeyondCompare or meld or… vim… can do simple comparisons in these cases.